Kinetics of Polymer Crystallization with Aggregating Small Crystallites

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Kinetics

Background:

• Poly(trimethylene terephthalate) (PTT) is a semi-crystalline polyester with unique properties.
• Understanding its crystallization behavior near the glass transition temperature is crucial for material processing and performance.
• Isothermal crystallization from the melt provides insights into polymer morphology development.

Purpose of the Study:

• To investigate the isothermal crystallization mechanism of PTT near its glass transition temperature.
• To analyze the kinetics and thermodynamics of crystalline aggregation region formation.
• To correlate PTT crystallization with established theories of polymer crystallization.

Main Methods:

• Wide-angle X-ray Diffraction (WAXD) for crystalline structure analysis.
• Small-angle X-ray Scattering (SAXS) for morphology and aggregation region characterization.
• Optical Microscopy for visual observation of crystallization patterns.

Main Results:

• Crystallization involves crystalline nodules forming aggregation regions that cover the sample.
• Kolmogorov-Johnson-Mehl-Avrami theory indicates three-dimensional homogeneous nucleation for aggregation regions.
• Sekimoto's theory analysis reveals growth velocity and nucleation rates of aggregation regions.
• Temperature dependence of growth velocity and nucleation rate aligns with spherulitic crystallization, suggesting precursor existence.

Conclusions:

• The crystallization mechanism of PTT near Tg is characterized by nodule formation and aggregation.
• Homogeneous nucleation governs the formation kinetics of these aggregation regions.
• Observed growth velocities and nucleation rates suggest precursors at the crystal growth front.